The invention relates to the field of damping in load-carrying members, particularly those load-carrying members that carry a load between a plurality of masses that are subject to induced cyclic distortion or vibration.
The invention applies to damping in any of a number of mechanical devices that carry a load between two masses. The invention is particularly useful for damping in vehicle braking systems. Vehicle braking systems are one of a class of mechanisms that can be induced to vibrate by the action of friction. In some situations, the vibration may become unstable and grow to levels severe enough to cause excessive noise, passenger discomfort, and/or structural failure of system components. Part of the art of designing such systems lies in increasing the stabilizing effects of damping within and between the components of the system to counteract the destabilizing effects of braking friction.
The wheel and brake assemblies of an aircraft landing gear system are an example of a vehicle braking system that are subject to friction-induced vibration of various system components during braking. Aircraft brakes generally have a structure called a "torque tube" that transfers brake disk generated torque to the brake housing, and thence to the landing gears. In landing gears having more than two brakes, the wheel and brake assemblies are typically mounted in pairs on two or more tandem axles, which are in turn fixed to a "bogie" or "truck" beam that pivots about a point on the inner cylinder of the landing gear's shock strut. The brake torque generated by each of the fore and aft wheel and brake assemblies is reacted by forces at its axle and through a brake rod that links the brake housing to the inner cylinder of the landing gear at a point above or below the bogie pivot. The fore brake rods act in compression and the aft rods act in tension to transmit braking forces to the bogie. For each assembly, the rod forms one of the four links of a parallel four-bar linkage that operates in the pitch plane of the aircraft.
The dominant modes of friction-induced vibration in aircraft brakes are "squeal" (a torsional oscillation of the non-rotatable brake parts) and "whirl" (a rotating bending oscillation). During both modes of vibration, an oscillating load is superimposed on the mean torsional load carried by the torque tube, and the mean compression or tension loads carried by the brake rods that may cause the rod to bend. Workers in the art have recently attempted to solve the brake vibration problem in various ways, including providing an axial coulomb damper in a brake rod. The brake rod essentially acts as a shock absorber. This solution was not entirely satisfactory. In addition, the torque tube may develop torsional and/or bending modes of vibration, and other components may also be induced to vibrate. Therefore, means of reducing or eliminating friction-induced vibrations are generally desired. Copending application Ser. No. 08/592,816 now U.S. Pat. No. 5,806,794 entitled "Aircraft Braking System With Damped Brake Rod" and copending application Ser. No. 08/559,354 now U.S. Pat. No. 5,915,503 entitled "Brake Rod Having a Bending Mode Coulomb Damper" are directd to damped brake rods.
The invention disclosed herein is a simple, lightweight, inexpensive, and effective solution to the brake vibration problem. However, it is not intended to limit the invention to application in aircraft brakes and landing gear, or friction-induced vibration, as improved damping devices are generally desired in the mechanical arts. The invention is useful for damping vibration in many types of load carrying members.